This invention relates generally to nuclear reactors, and more particularly to a service platform for use in a nuclear reactor.
A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A top guide, sometimes referred to as a grid is spaced above a core plate within the RPV. A core shroud, or shroud, surrounds the core plate and is supported by a shroud support structure. The core shroud is a reactor coolant flow partition and structural support for the core components. Particularly, the shroud has a generally cylindrical shape and surrounds both the core plate and the top guide. A removable shroud head is coupled to a shroud head flange at the top of the shroud.
During refueling of a nuclear reactor, the majority of the servicing operations are performed from a bridge system that spans the refueling floor and the reactor and fuel storage pool cavities. These bridges typically have a straight four to eight foot wide walkway along their length and can be positioned above the reactor or refueling pool cavity. To clear the hand rails and other structures at the edge of the reactor cavity or service pools, the refuel bridge must be elevated about five feet above the floor surface.
In use, the bridge is moved to the desired position above the reactor and personnel work along the walkway of the bridge. When working over a round reactor vessel such as a boiling water reactor, access to a specific azimuth zone of the round reactor vessel is restricted for any given placement of the bridge because of shape of the bridge. With existing bridge access, the number of work activities, and number of personnel that can perform work at the same time is limited. The use of refuel bridges and auxiliary bridges is the most efficient known method of work access for achieving productivity for plant outage schedules.
The type of work required to service a nuclear plant would be enhanced by access to the reactor along the radial and tangential directions of the vessel or component. A normal bridge system can only accomplish radial or tangential alignment at the specific azimuth positions of 0, 90, 180, or 270 degrees. Radial and tangential alignment can never be accomplished simultaneously. Therefore, personnel and equipment may not have the optimal angle of access for visual observation or equipment manipulation.